1. Field of the Invention
The invention relates to a system for reclaiming mined land, particularly land surface mined for extraction of phosphate values. The land surface to be mined is divided into contiguous parallel rows, and alternate rows are mined sequentially. Specially treated backfill is generated in the present invention to fill the row previously mined. The treatment process uses a thickener device which treats the sandy component and the slime component remaining in a large excess of water after extraction by water of the phosphate component. The thickener extracts water from the output of slime component for reuse or conservation, and additionally fills voids within the sandy component with the slime component to further reduce the volume of output.
2. Description of the Prior Art
Separation of solids and liquids by flocculation, filtration, settling, sedimentation, and decantation is known in the prior art. For example, Robinson in U.S. Pat. No. 1,855,610 shows a honeycomb arrangement for purifying a liquid with a suspended clay, where an upper overflow free of clay is removed from a filtering cylinder. Solid-liquid separation is also shown by Rice et al in U.S. Pat. No. 3,615,025 by use of a tube bank. Bounin in U.S. Pat. No. 2,816,660 discloses passing a grid or screen at very low speed through a flocculated mass for decanting liquid suspensions. Radial feed pipe lines for a thickener tank having a rotating rake are shown by Adams in U.S. Pat. No. 2,069,989.
Other patents showing aspects of prior art arrangements for separating suspended solids from liquids are the following:
U.S. Pat. No. 1,983,894--Dec. 12, 1933 PA1 U.S. Pat. No. 2,009,559--July 30, 1935 PA1 U.S. Pat. No. 2,047,798--July 14, 1936 PA1 U.S. Pat. No. 2,274,361--Feb. 24, 1942 PA1 U.S. Pat. No. 2,763,371--Sep. 18, 1956 PA1 U.S. Pat. No. 2,861,692--Nov. 25, 1958 PA1 U.S. Pat. No. 2,878,935--Mar. 24, 1959 PA1 U.S. Pat. No. 2,963,157--Dec. 6, 1960 PA1 U.S. Pat. No. 3,067,878--Dec. 11, 1962 PA1 U.S. Pat. No. 3,292,788--Dec. 26, 1968 PA1 U.S. Pat. No. 3,374,885--Mar. 26, 1968 PA1 U.S. Pat. No. 3,412,863--Nov. 26, 1968 PA1 U.S. Pat. No. 3,578,586--May 11, 1971.
Prior systems for separating liquids from suspended solids have failed to provide a means for simultaneously accomplishing dewatering of a suspension and filling of voids in a filtering material. Only by accomplishing both functions can a backfill material be generated which fills mined areas with a stable and agronomically sound soil. Furthermore, none of the patents shows a method of dividing a mined area into rows, followed by mining alternate rows and depositing the treated back fill in the previously mined row. Consequently, prior art treatments of the products of phosphate separation have yielded a product with substantially greater volume than the extracted material, necessitating dams or other impounding techniques for storing such materials, with consequent hazards of dam failure and a high rate of water consumption.